NaSICON (Na Super Ion CONductor) is a ceramic material with a nominal composition of Na1+xZr2P3-xSixO12 known to selectively transport sodium ions at extremely high rates (>10−3 S/cm at room temperature) through atomic channels formed between zirconia octahedra and phosphate or silica tetrahedra within its crystal structure. Depending on the chemical and crystallographic modifications of these materials, they can be engineered to selectively promote or inhibit ion transport based on ion size or charge, making this a particularly versatile and potentially important ceramic material system. Although NaSICON in its varied forms has found widespread application in energy storage, chemical separations, sensors, and other technologies, it suffers from potentially significant chemical instabilities. One of the potential sources of instability in these materials, particularly in aqueous environments, is the Zr—O bonds that make up much of the NaSICON lattice structure. For example, in pure zirconium oxide systems these materials would be expected to be significantly soluble in both acidic (below pH 4) and basic (above pH 12) environments. This instability prevents these types of materials from finding significant applications, for example as separators for alkaline sodium battery chemistries.
According to the present invention, the introduction of cationic substitutions for the Zr ion can stabilize these ceramic materials under these environments, potentially expanding their applicability.